Osteoclasts are cells generated by differentiation of bone marrow cells and known to be involved in a number of diseases such as osteometastasis of cancer cells including breast cancer cells, rheumatoid arthritis, and osteoporosis. Accordingly, it is presumed that successful suppression of the differentiation from bone marrow cells into osteoclasts will result in excellent therapeutic effects on the aforementioned diseases. Thus, it has been desired to develop substances that have low toxicities and exhibit potent inhibitory effects against the differentiation from bone marrow cells into osteoclasts. However, no reports have been issued until now on substances having such properties as mentioned above among low molecular weight substances derived from microorganisms.